The following description of the background of the invention is provided to aid in understanding the invention but is not admitted to be prior art to the invention.
Cellular signal transduction is a fundamental mechanism whereby external stimuli that regulate diverse cellular processes are relayed to the interior of cells. One of the key biochemical mechanisms of signal transduction involves the reversible phosphorylation of proteins, which enables regulation of the activity of mature proteins by altering their structure and function.
The best characterized protein kinases in eukaryotes phosphorylate proteins on the alcohol moiety of serine, threonine and tyrosine residues. These kinases largely fall into two groups, those specific for phosphorylating serines and threonines, and those specific for phosphorylating tyrosines. Some kinases, referred to as “dual specificity” kinases, are able to phosphorylate on tyrosine as well as serine/threonine residues.
Protein kinases can also be characterized by their location within the cell. Some kinases are transmembrane receptor-type proteins capable of directly altering their catalytic activity in response to the external environment such as the binding of a ligand. Others are non-receptor-type proteins lacking any transmembrane domain. They can be found in a variety of cellular compartments from the inner surface of the cell membrane to the nucleus.
Many kinases are involved in regulatory cascades wherein their substrates may include other kinases whose activities are regulated by their phosphorylation state. Ultimately the activity of some downstream effector is modulated by phosphorylation resulting from activation of such a pathway.
The serine/threonine kinase family includes members found at all steps of various signaling cascades, including those involved in controlling cell growth, migration, differentiation and secretion of hormones, phosphorylation of transcription factors resulting in altered gene expression, muscle contraction, glucose metabolism, control of cellular protein synthesis, and regulation of the cell cycle.
Chromosomal abnormalities are a hallmark of human cancer, reflecting the deleterious consequences of the gain or loss of genetic information (Mitelman et al., Nature Genet. 15:417-474, 1997; Hartwell et al., Science 266:1821-1828, 1994). Some of these defects may have a causal role in cellular transformation due to loss of a negative growth regulator, loss of a gene responsible for maintenance of genome integrity, or through the amplification or activation of an oncogene (Kinzler et al., Nature 386:761-763, 1997; Hunter Cell 88:333-346, 1997). Alternatively, these abnormalities may be a consequence of tumor progression where mitotic checkpoints have been disrupted, resulting in abnormal nuclei, miss-segregated chromosomes, and aneuploidy (Elledge Science 274:1664-1672, 1996; Sherr Science 274:1672-1677, 1996).